The class of chemical war-threat agents known as vesicants include among others arsenicals and mustard agents. Stockpiles of weaponized arsenic-based vesicants developed for World War II still exist. Recently, vesicants have been used against civilian populations in Iraq and Syria and caused extensive morbidities and a few casualties. Cutaneous exposure to arsenicals causes vesicular skin lesions, blisters, and painful cutaneous inflammation, which progresses to multi-organ tissue disruption and death. Four major arsenicals, lewisite, diphenylchlorarsine, diphenylcyanoarsine and diethylchloroarsine, have been identified as potential threat chemicals by NIH CounterACT program for which antidotes/agents are highly sought. However, the mechanisms by which these arsenicals manifest such robust deleterious effects in the skin remain undefined. We have recently developed a highly sensitive murine model of cutaneous arsenical exposure, which recapitulates skin pathology of humans exposed to these chemicals. Our preliminary studies indicate that the acute inflammatory and tissue damaging effects caused by arsenicals are mediated through the rapid onset of epigenetic modifications and chromatin remodeling via histone lysine hyperacetylation. In this regard, bromodomain 4 (BRD4), a reader of histone acetylation marks is considered to be one of the potent transcriptional regulator of inducible inflammatory genes besides others. In this Project-I of U54, we propose to investigate histone acetylation-based epigenetic alterations involved in the molecular pathogenesis of skin lesions and development of antidotes that can block arsenical-induced cutaneous injury. Three specific aims are proposed: 1: To characterize histone acetylation and chromatin remodeling-associated with arsenical exposure. This data will provide a correlation between the spatiotemporal regulation of histone acetylation and underlying arsenicals- induced cutaneous injury. After establishing these changes in murine skin we will confirm the molecular pathogenesis of acute skin injury by arsenicals in minipig; 2: To unravel the molecular mechanism by which arsenicals-mediated histone acetylations affect inflammatory and blistering responses. We will probe the mechanisms by which arsenicals induce BRD4 activation. 3: To define the window of therapeutic intervention of arsenicals-mediated tissue damage by administering BRD4 inhibitors. Our goal is to fully characterize the kinetics of action and assess the therapeutic window of time (30, 60 or 120 min after exposure to arsenicals) in which these BRD4 inhibitors are able to reverse arsenical-induced molecular changes and underlying skin inflammation/blistering. This project will integrate with projects II, III, and scientific cores as animal tissues will be shared from topically exposed animals. Therapies successful in reversing skin inflammation/damage will also be verified for the diminution of lung and kidney injury. Successful completion of this proposal will lead to a paradigm shift in the existing knowledge of arsenicals' toxicity and development of novel series of mechanism- based antidotes.